1. Field of the Invention
The present invention relates to a method of planarizing a first pole piece layer of a write head by lapping without delamination of the first pole piece layer from the wafer substrate and, more particularly, to a step before lapping wherein intrinsic stress of a full film first pole piece material layer is relieved before lapping.
2. Description of the Related Art
A magnetic head assembly typically includes write and read heads wherein the write head writes magnetic bits of information into a rotating magnetic disk in a disk drive and the read head reads the magnetic bits of information from the rotating disk. The write head includes first and second pole piece layers which have a yoke region between a pole tip region and a back gap region. An insulation stack with a write coil layer embedded therein is located between the first and second pole piece layers in the yoke region, the first and second pole piece layers are separated by a nonmagnetic write gap layer at an air bearing surface (ABS) which faces the rotating disk and the first and second pole piece layers are magnetically connected in the back gap region.
The read head includes a spin valve sensor and first and second lead layers that are connected to first and second side edges of the spin valve sensor for conducting a sense current therethrough. The spin valve sensor and the first and second leads are located between nonmagnetic electrically conductive first and second read gap layers and the first and second read gap layers are, in turn, located between ferromagnetic first and second shield layers. In a merged magnetic head assembly the second shield layer and the first pole piece layer are a common layer whereas in a piggyback type magnetic head assembly these are separate layers which are separated by a nonmagnetic layer.
The initial steps in a typical method of making a read head is to form the first shield layer followed by sputter deposition of the first read gap layer on the first shield layer. Next, the read sensor and first and second hard bias and lead layers are formed with the first and second hard bias and lead layers connected to first and second side edges respectively of the sensor. After these steps, the first and second hard bias and lead layers have a profile which is higher than the top surface of the read sensor which, in cross section, has the configuration of a dip where the sensor is located. Next, the second read gap layer is sputter deposited on the sensor and on the first and second hard bias and lead layers resulting in the second read gap layer replicating the dip above the sensor. In a merged magnetic head a second shield/first pole piece layer is plated on the second read gap layer resulting in the second shield/first pole piece layer replicating the dip directly above the read sensor. In the construction of the write head the insulation stack is formed on the second shield/first pole piece layer in the yoke region and a write gap layer is formed on the second shield/first pole piece layer in a pole tip region. Next, the second pole piece layer is formed on the write gap layer, the insulation stack and is connected to the second shield/first pole piece layer in the back gap region.
Unfortunately, the write gap layer also replicates the dip directly above the read sensor which seriously degrades the performance of the write function of the write head. The dip in the write gap is referred to in the art as write gap curvature. When the write head writes magnetic bits of information into a rotating magnetic disk the bits are curved. When the read head, with its linearly extending sensor, reads the magnetic bits of information there is signal loss due to upwardly extending end portions of the magnetic bits of information which are not sensed by the read sensor. Accordingly, there is a strong-felt need to overcome the problem of write gap curvature.
It should be understood that multiple magnetic head assemblies arranged in rows and columns on a substrate for simultaneous construction. Accordingly, in constructing the second shield/first pole piece layer multiple second shield/first pole piece layers are constructed above respective sensors of rows and columns of read heads. Before plating a full film second shield/first pole piece material layer across the entire wafer a photoresist frame is formed masking the perimeters of the desired shape of the second shield/first pole piece layer for each magnetic head assembly. Accordingly, this perimeter defines where plating of the second shield/first pole piece layer will not occur during the plating step. Surrounding each perimeter will be a comparatively large field region where second shield/first pole piece material will be deposited. After forming the photoresist, which is referred to in the art as the resist frame, the second shield/first pole piece full film layer is plated on the wafer substrate. The resist frame is then removed leaving discrete second shield/first pole piece layers above each respective read sensor with the aforementioned second shield/first pole piece material layer portions in the field.
After plating the full film second shield/first pole piece layer on the wafer substrate the second shield/first pole piece material layer portions in the field are etched away leaving the discrete second shield/first pole piece layer for each magnetic head assembly. Next, the second read gap and the first read gap layers are etched away in the field leaving the first and second read gap layers directly below the second shield/first pole piece layer of each magnetic head assembly. This is followed by etching the first shield layer of each magnetic head assembly away in the field, leaving the first shield layer generally with a larger lateral expanse than the second shield/first pole piece layer.
In the construction of the write head a first insulation layer of the insulation stack is formed on the second shield/first pole piece layer in the yoke region. This layer is typically made of baked photoresist and extends across the width of the second shield/first pole piece layer and then laterally off of first and second side edges of the second shield/first pole piece layer in first and second laterally extending field regions beyond the first and second side edges. Accordingly, the first insulation layer has a high profile on top of the second shield/first pole piece layer and has depressed portions in the first and second laterally extending field regions. Unfortunately, when a pancake-shaped write coil is constructed on top of the first insulation layer of the insulation stack, it likewise has a high profile directly above the second shield/first pole piece layer and first and second depressed portions in the first and second field regions beyond the first and second side edges of the second shield/first pole piece layer. This results in a poorly formed write coil layer because of first and second steps at the first and second side edges of the second shield/first pole piece layer as it makes its transition from a high profile above the second shield/first pole piece layer into the first and second field regions. The write coil is typically copper (Cu) and is frame plated on the first insulation layer of the insulation stack. The photoresist layer that forms the resist frame has poor definition as it drops down from the high profile to the lower profiles in the first and second shield regions which can cause poorly shaped side walls of the write coil in the downwardly sloping regions and a thinning of the thickness of the turns of the write coil as these turns slope down from the high profile to the lower profile first and second shield regions.
As described hereinabove, the magnetic head assemblies are constructed in rows and columns on a wafer substrate. After completely forming the magnetic head assemblies on the substrate, the substrate is cut into rows of magnetic head assemblies whereupon each row is lapped to form an air bearing surface for each of the magnetic head assemblies. The row is then cut into individual magnetic head assemblies. This leaves each magnetic head assembly located on a cut portion of the wafer substrate which forms the aforementioned slider. Before the cutting operation at the wafer level the rows and columns of magnetic head assemblies are, in reality, rows and columns of slider sites upon which a magnetic head assembly is formed within each slider site. Each slider site at the surface of the wafer substrate is, in reality, a respective trailing edge of a slider after the cutting operations. The slider sites, which are typically rectangular on the surface of the wafer substrate, are immediately adjacent one another wherein each slider site has perimeter portions which are shared with at least two other immediately adjacent slider sites.
Accordingly, before removal of the first and second shield/first pole piece material layer portions, the second and first read gap portions and the first and second field portions of the first shield layer, photopatterned second shield/first pole piece layer within each slider site has a perimeter which is separated by the photoresist from field portions of the second shield/first pole piece material layer about the second shield/first pole piece layer. The field regions of the second shield/first pole piece material layer about each second shield/first pole piece layer is continuous. After photopatterning the second shield/first pole piece layers within each slider site the top of the wafer substrate appears as rows and columns of photopatterned second shield/first pole piece layers within a sea of second shield/first pole piece material in the fields of all of the slider sites. An understanding of this arrangement is important in understanding the present invention which is described under the summary of the invention.